I wrote a tool a while back to convert the .xml texture-atlas tilesheets that come with the Asset-downloads to .JSON format. I used this because I didn't know an easy way to use the .xml files in js/html5 projects. If there is an easy way, you can ignore this :-)
https://bewelge.github.io/TextureAtlastXMLtoJSON/
It should work for multiple files at once. If it doesn't work, there are a couple of others if you google. I remember using this PHP script once and it worked just fine:
https://github.com/snollygolly/TextureAtlasConverter
Enjoy the Jam everyone ;)